The invention concerns a process for the preparation of lead and zinc cyanurates from PbO or ZnO, respectively, and cyanuric acid. The reaction of the respective oxides with cyanuric acid takes place in an aqueous paste mixture without the addition of catalysts.
According to the U.S. Pat. No. 4,329,381, lead and zinc cyanurates are used in corrosion-inhibiting coatings for metal surfaces. They can be prepared according to this patent by suspending lead or zinc oxide and cyanuric acid in boiling water, to which acetic acid must be added as catalyst to accelerate the reaction. The cyanurates precipitate from the aqueous solution and must be filtered, washed and dried.
One disadvantage of this process is the low solids content of these suspensions, which in order to remain stirrable may not exceed a maximum of 14% for zinc cyanurate and 20% for lead cyanurate. This results in high production costs. Secondly, the salt must not contain any foreign ions if they are to be used as corrosion inhibiting coatings. Consequently, an expensive washing process is needed for the removal of acetic acid when added as a catalyst.